The elevation of the tailwater at the culvert outlet.
The type of inlet. Except for drop inlets, the type of inlet is not generally considered in military culvert
design.
Remember that the discharge capacity of a culvert will be increased, particularly in short culverts on steep slopes,
by a smooth-transition type of inlet.
The Theory of Closed Channel Flow, like the principles of open channel flow, holds with the conservation of
mass; that is, it assumes that the flow is continuous, that there is no ponding, and that the flow occurs at crown
elevation (free flowing). Therefore, neither the inlet nor outlet can be submerged. To design a pipe with a given
Q the engineer must take into consideration four factors:
Friction (Manning's roughness coefficient, "n")
Area
Slope
Head (the difference in elevation between each end of the culvert)
PART B - FOUR TYPES OF CULVERTS
Culverts are classified as either permanent or expedient (improvised).
In this lesson we are concerned with four types of pipe: CMP, concrete pipes, concrete box culverts, and
expedient.
CMP
CMP is available in the diameters and gauge listed. It comes in nestable half-sections that, when assembled, give
two-foot effective lengths. The following construction techniques should be used in the installation of CMP:
First, the joints should be lapped so the water flows over and not through the joint, preventing possible
saturation of the compacted fill. A saturated soil loses strength and the culvert could fail by crushing.
Figure 5-2, page 5-4 demonstrates how the length should be assembled.
5-3
EN5465
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